The invention is in the field of digital image processing and particularly concerns a parameterized process for obtaining the Radon transform of a digital image having a raster-scanned format.
In image display technology, a raster display presents an image as a set of component picture elements ("pixels" or "pels"). The raster forming the image includes an array of pixels arranged generally into horizontal raster lines or rows of pixels. Columns are also defined on the raster, thereby establishing a two-dimensional matrix of pixels which fill the image display area. The image is generated by scanning the picture elements sequentially, line-by-line from a top corner of the display area to the bottom diametric corner. The process then repeats by retracing to the top corner of the matrix.
A raster scan image on a display area is formed by modulation of a beam which is scanned over the raster, with the intensity of the beam being modulated at each pixel location according to the contribution which the pixel makes to the entire image.
In the representation of an image by a digitized raster, storage is provided in the form of a pixel map which generally has a one-to-one correspondence between individual storage locations and pixel locations in the raster. Each pixel storage location contains a multi-bit digital representation (usually, a byte) of image intensity at the pixel location.
The raster format of a digitized image supports high-speed processing of the represented image by any of a number of discrete transform methods which produce intermediate information forms amenable to such processing. Among the best known is the discrete fourier transform (DFT) which can be conveniently implemented in a pipelined architecture to obtain high-speed transformation of a digital image to fourier space.
An especially important transform employed for the analysis of a digitized image is the Radon transform which is applied in medical diagnosis, for example, in the form of computerized tomography. Other applications of the Radon transform in which a two-dimensional object is reconstructed from a set of one-dimensional projections, include radio astronomy, electron microscopy, optical interferometry, and geophysical exploration. Recently, the Radon transform has also been shown to offer advantages for general image processing, in which a digital image must be transformed into Radon space. The significant impact on various machine vision problems of Radon space representation and manipulation has been shown, for example, in the publication by J. L. C. Sanz, et al., entitled "Radon and Projection Transform-Based Computer Vision", Springer-Verlag, 1988. This publication teaches the rapid computation of an approximation to the Radon transform of digital images In Ohyama, et al "Discrete Radon Transform in a Continuous Space", JOSA, February 1987, pp. 318-324, it is asserted that use of a translated rectangle function to synthesize the Radon projection of an image gives an exact result. Therefore, an apparatus and procedure that produces an exact result of the Radon transfer for an image model that consists of a translated rectangle would be a welcome advance in the art.